A seminal method to determine the state of polarization of a light beam using measurable quantities is the Stokes method, which involves four independent intensity measurements of the light beam. Each measurement corresponds to the intensity of the beam after it passes through each of four different filter system arrangements. The four Stokes parameters, sometimes called S0, S1, S2 and S3, are derived from these four measured intensities and form a four-element column vector in four-dimensional mathematical space.
Since the discovery of the Stokes method in 1852, many filter systems based thereon have been presented. Extracting polarization information from images is not new either. However, four separate images are used to calculate the Stokes parameters for each element in a scene. To date, a major problem still exists in using the Stokes method for acquiring polarization information from images. The problem occurs because it takes time to capture separate images. In the time it takes to acquire each image, the intensity or polarization state of points in the scene may change. This time factor would affect polarization measurements taken outdoors where changing sun position or cloud conditions would change the intensity or polarization state of the light entering the filter system. In the laboratory, temperature, pressure, density or concentration variations associated with scene elements may change the polarization state of the light entering the filter system during the time required to record four separate images.